For stat. points, x + 512 - 2x^2 = 0
But when i factorise that using the quadratic formula for 0 i get a figure with a surd in it...
Im pretty sure if i continue with it it wont produce the 64cm^2 that is the answer

My intercept value is not the same as yours for the side, you are missing an a. So your value for the Area is . Is this the value you had? The diffriation for this is quite complicated as well, if you want to see a sample diffrentiation try:http://www2.wolframalpha.com/Calcula...=3&w=461&h=874

For problem B:

The answer you are looking for will have a surd in it. Remember that the value the equation gives you is the value for x, not the value for the area. To get the cvalue for the area (th 64 cm^2) you have to work out your y (from and then get your area from

With regards to your diffrentiation itself:
chain Rule: with and
To get the you use the product rule. where , and (Do you how this works?)

which leaves
Simplifying gives

You only care when A'=0, so this simplifies to .

Finally, to get the area you plug your x and y obtained above into A=0.5xy. That help?